1. Field of the Invention
The present invention relates to a switch in which contact points are arranged in a switch case formed of a substrate and a lid body.
2. Description of Relevant Art
An example of this kind of switch includes a neutral start switch attached to a select lever for a vehicular automatic transmission. The neutral start switch is typically configured such that a switch case is formed of a plastic substrate and a plastic lid body, fixed contact points are arranged in the substrate, and movable contact points are arranged in a movable board movably arranged in the switch case. The substrate is formed in a fan shape and has a shaft hole penetrating therethrough at the rotational center thereof. A plurality of rows of fixed contact points, formed in an arc shape around the shaft hole, is arranged on the substrate. The fixed contact point has a connecting piece portion extending within the substrate by insert molding, and a tip end of the connecting piece portion is exposed as a terminal to a connector portion formed integrally with the substrate.
In this switch, the movable contact point slides along the fixed contact point while keeping the contact with the fixed contact when the movable board turns around the shaft hole, and thereby a switching operation is performed. Seal rings are provided between a shaft of the movable board and the shaft hole such that water, mud or the like does not enter into the switch case in which the fixed contact point and the movable board are arranged. In a joint portion between the substrate and the lid body, a seal ring is provided and a joint structure by welding is adopted. An example of the joint structure by welding includes a share joint method. In a case of the neutral start switch, the share joint method high in the welding degree is used in view of requiring high joint strength between the substrate and the lid body for certainly maintaining the sealed condition in the inside of the switch.
FIGS. 9A to 9D show the jointing process of a joint structure between a substrate 10 and a lid body 35 in a case of welding them by the share joint method. As shown in FIG. 9A, a side wall 12 of the substrate 10 is closed by surrounding an entire circumference of a rotary region of the movable board (not shown). A ring groove 30 which accommodates a seal ring 31 therein and a concave streak portion 26 are formed on a top surface 25 of the side wall 12. The ring groove 30 and the concave streak portion 26 are formed in this order from the inside and are provided along the entire length of side wall 12. A welding inclination surface 27 is formed in the concave streak portion 26 of the side wall 12 at an outer peripheral side in the depth portion thereof. In addition, the lid body 35 is provided with a projecting portion 40 on a lower surface 38a of a flange portion 38. The projecting portion 40 is provided at the position opposing to the top surface 25 of the substrate 10, and extends in the entire circumference along a peripheral edge of the flange portion 38 to close the lid body 35. The projecting portion 40 is fitted in the concave streak portion 26 of the side wall 12 when assembling the switch case.
A welding shoulder portion 41 is formed in the projecting portion 40 at the outer peripheral side in the intermediate position thereof. When the top surface 25 of the side wall 12 makes contact with the lower surface 38a of the lid body 35, the welding shoulder portion 41 of the projecting portion 40 is designed to interfere with the welding inclination surface of the concave streak portion 26. As a result, high-frequency welding causes melting of the interference portion, so that the projecting portion 40 and the side wall 12 are jointed along the entire circumference. For example, Japanese Patent No. 4509370 discloses the configuration as similar to the above.
In the aforementioned joint structure, when the projecting portion 40 of the lid body 35 is in the process of being inserted into the concave streak portion 26 of the substrate 10 while interposing the movable board (not shown) between the substrate 10 and the lid body 35, as shown in FIG. 9B a corner of the welding shoulder portion 41 of the projecting portion 40 first makes contact with the welding inclination surface 27 of the concave streak portion 26. In this state a gap S1 remains between the top surface 25 of the side wall 12 and the lower surface 38a of the lid body 35. The ring groove 30 has a depth smaller than a diameter of the seal ring 31 in a free state, and the seal ring 31 partly projects from the ring groove 30.
As the lid body 35 is further pressed to the substrate 10 from a position of FIG. 9B in the high-frequency applied state, the interference (overlap) portion between the welding shoulder portion 41 and the welding inclination surface 27 is welded while melting the interference portion. Thereby, the lid body 35 moves in the approaching direction relatively to the substrate 10.
In addition, as shown in FIG. 9C after the lower surface 38a of the lid body 35 makes contact with the seal ring 31 in the ring groove 30, it presses the seal ring 31, and finally, as shown in FIG. 9D, the lower surface 38a is seated on the top surface 25. Therefore the projecting portion 40 and the side wall 12 are jointed along the entire circumference by welding, and together with the sealing operation between the seal ring 31 and the lower surface 38a, the inside of the switch case becomes in a sealing condition to an outside.
In this kind of switch, generally a contact-point grease is applied to the contact point of the switch for improving endurance and current-carrying properties at contacting of contact point. But, in the sealed type of switch as descrambled above, there occurs the event that the connector portion around the terminal is wet with oil.
According to the study on the cause of the above event, the following point is found out. In case of the switch discussed above, the conductive-metallic fixed contact point is insert-molded to the plastic substrate. However, since a perfectly adhesive state is not formed between the fixed contact point and the plastic, the grease on the fixed contact point flows along the interface between the fixed contact point and the plastic and leaks into the connector portion.
This event is supposed to occur because a pressure in the switch case is higher than the outside pressure, and therefore the grease is pushed out through the interface between the fixed contact point and the plastic. That is, in the jointing process between the substrate 10 and the lid body 35, an inner space interposed between the substrate 10 and the lid body 35 is blocked out from the outside when the lid body 35 reaches at the position shown in FIG. 9B. Then, the inner space is compressed in a height direction by the height of gap S1 when the lid body 35 is pushed to the substrate 10 from the position in FIG. 9B to the position in FIG. 9D. In this case, since the welding shoulder portion 41 and the welding inclination surface 27 are welded with each other to increase the welding amount, the welding strength is increased. However, the pressure in the inner space becomes greatly higher than the outside pressure. Here, the region between the shaft portion of the movable board and the shaft hole is also sealed by the seal ring. Accordingly, also after the switch is mounted on the automatic transmission or the like as a product, the higher-pressure state is held in the switch case than that of the outside. Therefore the grease applied on the fixed contact point of the substrate before the substrate is jointed to the lid body is exposed to this high pressure.
Therefore, it has been required to provide a switch which prevents water, mud and the like from entering into a switch case and at the same time, reduces a pressure in the switch case for preventing leakage of grease into a connector portion.